MOLLUSKS 119 
“plate gills,” and the gills of a clam or oyster bear a close super- 
ficial resemblance to a pair of delicate leaves on each side of the 
body. In some of the lamellibranchs, however, the gills consist of 
delicate filaments calling to mind the barbules of a feather. Gills 
of this sort are seen in the jingle shell (Anomia), the bloody clam 
and in mussels. In oysters and clams, however, the feathery fila- 
ments are fused one to another at many points, leaving sieve-like 
openings through which water may pass in its course through the 
gills. The gill sheets are also fused to the mantle, thus forming a 
chamber through which the waste water from the gills passes 
alomg the sides of the body on its way to the excurrent tube of the 
siphon. The water current over the gills is maintained by the 
orderly and constant beating of vast numbers of cilia that cover 
their surfaces. 
Lamellibranchs feed upon minute organisms, both animal and 
vegetable. This food is drawn in with the water currents, and is 
caught upon the slime of the gills, and then driven toward the 
mouth by the movements of the cia. There it is collected upon 
the curtain-like lips, and driven by their cilia into the alimen- 
tary tract. 
There is a fairly well developed stomach which is surrounded 
by a large liver, the duct of which empties into the stomach. A 
long gelatinous rod called the crystalline stylet is often found in 
the stomach, but its exact nature and function are unknown. The 
intestine is twisted, and is surrounded by the genital organs. 
The heart is three-chambered, and the hind-gut passes through 
it. It pumps blood from the gills to other parts of the body. 
The Lamellibranchiata are sedentary creatures and many of 
them remain fixed from the end of their larval development until 
death, as is the case with the oyster. A few, such as the scallop, are 
enabled to swim in an awkward darting manner by the rapid 
closure of their valves, thus driving the animal hinge-side forward. 
Others, such as the clams, are enabled to burrow through sand and 
mud by means of their muscular foot, while still others, such as the 
mussels, drag themselves slowly about by means of their byssus 
threads. 
As one would expect in such slow moving creatures, sense or- 
gans are poorly developed. On the mantle edge of the scallop, 
